Manampitiya Mahaweli Ganga water level

Expected to stay below alert level for the next 24 hours.

Published as 0.63 m (alert 3.0 m, minor flood 4.3 m, major flood 6.0 m)

Elevated river-flow outlook this week.

• Alert (9.8 ft): unlikely, about 1 in 10
• Minor flood (14.1 ft): unlikely, about 1 in 10
• Major flood (19.7 ft): unlikely, about 1 in 10

Rain that fell

0.0 mm in the last 3 hours, 15 mm in the last 24 hours at this gauge (moderate rain)

Rain forecast

6.8 mm in the next 24 hours over the catchment (light rain). Forecast model estimate.

Satellite estimate of rain over the catchment: 6.5 mm in the last 6 hours, 40.6 mm in the last 24 hours (to 12:30 am). It can differ from the gauges. GSMaP data by Japan Aerospace Exploration Agency (JAXA)

• · Outlook: the GloFAS global flood model has river flow at 1806 m3/s in its highest member within 7 days, above the 1-in-20 level (732 m3/s). This is a heads-up only; it does not change the levels above.
• · Part of the range is above the highest level this model has seen (4.6 ft); treat it as a rough guide.

• How this is worked out
• · Latest level at Manampitiya and recent change. No gauge sits upstream of it (or none reports in step with it), so the catchment rain is its upstream signal.
• · Forecast model estimate of catchment rain (Open-Meteo, area average over 29 grid cells above Manampitiya): 43 mm modelled for the last 24 hours, 7 mm forecast for the next 24 hours, with ECMWF ensemble spread.
• · The 1, 3, 6, 12, 24 hour steps use this gauge's own recent changes and the other gauges on the river (fitted to about 11 months of hourly readings, including the November 2025 Ditwah floods); where this was tested against 'level stays the same' it missed by less.
• · The 1, 3, 6, 12, 24 hour steps read the rain the satellite measured over Manampitiya's catchment (JAXA GSMaP, corrected for how it reads here), with rain beside the gauge and rain on the channels upstream timed separately (about 4 h from beside the gauge, about 16 h from upstream). Tested storm by storm it was closer than the version that reads the weather model's rain.
• · Heavy rain upstream is part of the 1, 3, 6, 12, 24 hour steps: rain that has fallen or is forecast over the catchment above Manampitiya raises the level, and the top of the range allows for the heavier forecast rain. Tested storm by storm (leaving each storm out, Ditwah included) it was closer than the river's own trend alone.